Influence of nonequilibrium quasiparticles in phonon imaging of superconductors: Consistency with BCS theory in Pb crystals

摘要: This paper is the second part of a study motivated by prediction Overhauser and Daemen A. W. L. Daemen, Phys. Rev. Lett. 61, 1885 1988 that electronic ground state Pb exhibits spin-density wave SDW leads to highly anisotropic superconducting gap. The first our J. D. Short, T. Head, P. Wolfe, B 78, 054515 2008 extended theoretical predictions actual Fermi surface initiated phonon imaging experiments on high purity Pb. temperature dependence absorption quasiparticles over 1.45–2.1 K range was found be much weaker than exp − o /kBT form using generally accepted gap parameter o=1.35 meV for In addition, coefficients obtained two crystals different thickness were not consistent with in thermal equilibrium lattice. To explain these anomalies context BCS theory superconductivity, we examine possible effects nonequilibrium generated laser source bolometer detector. Detailed varying crystal length, size, excitation power, pulse duration wide limits enable us isolate both thermal-equilibrium quasiparticles. variety data yields an quasiparticle density varies as =1.32 0.07 meV, good agreement inconsistent electronic-specific-heat van der Hoeven Keesom B. C. Hoeven, Jr. Keesom, 137, 103 1965 hypothesis summary, ballistic phonons provides unique measure agrees extending =2.6 10−5 at 1.45 K.